The long-term objective of this proposal is to test the hypothesis that factors, which promote the expression or activity of DN-p63 contribute to the preservation of self-renewal in basal epithelia, and factors that oppose the expression or activity of DN-p63 contribute to the forfeiture of self-renewing capacity. There is abundant evidence that DN-p63 is required for the preservation of self-renewal, however the precise mechanisms by which it achieves this have not been fully elucidated. We define self-renewal as the ability to retain proliferative capacity, resist differentiation signals and avoid developmentally regulated apoptosis. Several recent studies have indicated that cancer initiation is a condition of unregulated self-renewal. This underscores the importance of identifying the mechanisms that preserve and regulate self-renewal and defining the consequences of their subversion. Specific Aim 1 intends to evaluate the contributions of DNp63 to retention of proliferative capacity and resistance to cellular differentiation signals. Specific Aim 2 intends to evaluate the contributions of DN-p63 to resistance to apoptosis, and the role of DN-p63 in mediating an appropriate response to genotoxic stress. Specific Aim 3 intends to address the developmental consequences of forfeiture of self-renewal that is mediated by disruption of DN-p63. The goal of Specific Aim 3 is to identify and validate gene-regulatory events that result from disruption of DN-p63 and to determine if these events mediate the forfeiture of self-renewal. Our previous studies indicate that DNp63 is a direct target of p53, however genetic analysis of p53 has not indicated a self-renewal deficiency. Specific Aim 4 intends to identify and characterize a p53-independent mechanism that promotes expression of DN-p63, and to determine if this mechanism is responsible for p53-independent expression of DN-p63. Successful completion of these aims will offer insights into the molecular mechanisms underlying the decision of self-renewing basal progenitors to either preserve or forfeit self-renewing capacity.